“There was a first major blast from a car bomb, and then smaller explosions that appeared to be from rockets fired at the area subsequently,” he added.

Early on Monday morning explosions rocked an area close to the Mazzeh military airbase in Damascus' western suburbs.

The explosion was heard across parts of the Syrian capital, and flames were visible from a distance, said the Observatory, which relies on a network of activists, medics and lawyers on the ground for its information.

The number of bomb attacks in Damascus targeting military checkpoints, soldiers and government buildings have escalated in 2013.

On April 29, a car bomb exploded in Mazzeh targeting the car of Prime Minister Wael al-Halqi. He was unharmed but his bodyguards were killed.

More recently, twin suicide bombers targeted a police station in the city center on Tuesday last week, killing at least 14 people and wounding more than 30 others.

The Syrian revolution began with peaceful anti-government protests but has since escalated to a regional war that has drawn in Syria's neighbours and the wider international community. At least 93,000 Syrians have died since the conflict began in March 2011, according to a recent UN report.